because the button that launch the composer is actually a link (see https://github.com/mozilla-b2g/gaia/pull/16377/files#diff-56289627d91906a9c3b0f834ef19f514R90); eventually the link should be removed and we should use a real `<button type="button">` instead, and then we can remove this.

I can file a bug and add a comment here so that it's clearer.